[SI-LIST] Re: SpectraQuest Question.
- From: "Todd Westerhoff" <twester@xxxxxxxxxxx>
- To: <signalguy@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 13 Mar 2002 08:35:33 -0500
Josna,
When you specify a frequency for a "PULSE" stimulus in SQ, it creates a
clock of that frequency. So, for example, if you specified "200 MHz", yod
get a signal with a 5ns period (2.5ns high, 2.5ns low).
I prefer to talk about data rates according to the scheme of the signal used
to latch the data. In your case, I'm guessing that you're latching data off
the rising and falling edges of a 200 MHz clock signal (also known as
Double-Data Rate, or DDR). In that case, you'd specify the data signal as
200 MHz, because SQ simulates it as a clock.
In general, the rule for specifying data signal frequencies is:
SDR clocking = 1/2 the clock speed
DDR clocking = same as clock speed
When in doubt, I always just run a simulation and look at the waveforms. If
you know how long you expect between data bits, it's easy to figure out
whether the setting is right or not.
Hope that helps!
Todd.
Todd Westerhoff
Signal Integrity Engineer
Hammerhead Networks
5 Federal Street - Billerica, MA - 01821
email:twester@xxxxxxxxxxx - ph: 978-671-5084
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of fname lname
Sent: Tuesday, March 12, 2002 10:08 PM
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] SpectraQuest Question.
Hi folks,
I plan to do a simulation on a 400Mhz interface. The data signals toggle at
400Mhz with the two strobes running at 200MHz with base clock at 100MHz. Now
when setting up a simulation in SQ do I need to use the clock frequency as
400MHz or 200MHz.I am confused as to if the buffers toggle at 400Mhz or
200Mhz. I would really appreciate If some one can provide more insight into
this.
Thanks,
Josna.
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